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Further estimates of (T - T-90) close to the triple point of water.

Underwood, R; de Podesta, M; Sutton, G; Stanger, L; Rusby, R; Harris, P; Morantz, P; Machin, G (2017) Further estimates of (T - T-90) close to the triple point of water. Int. J. Thermophysics, 38 (3). p. 44.

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Recent advances in primary acoustic gas thermometry (AGT) have revealed significant differences between temperature measurements using the International Temperature Scale of 1990 (ITS-90), T 90 , and thermodynamic temperature, T. In 2015 we published estimates of the differences (T -T 90 ) from 118 K to 303 K, which showed interesting behaviour in the region around the triple-point of water, T_TPW = 273.16 K. In that work, the T_90 measurements below T_TPW used a different ensemble of capsule standard platinum resistance thermometers (SPRTs) than the T_90 measurements above T_TPW. In this work we extend our earlier measurements using the same ensemble of SPRTs above and below T TPW , enabling a deeper analysis of the slope d(T -T_90 )/dT around T_TPW.
In this article we present the results of seven AGT isotherms in the temperature range 258 K to 323 K. The derived values of (T -T 90 ) have exceptionally low uncertainties, and are in good agreement with our previous data and other AGT results. We present the values (T -T_90 ) alongside our previous estimates, with the resistance ratios W(T) from two SPRTs which have been used across the full range 118 K to 323 K. Additionally, our measurements show discontinuities in d(T -T 90 )/dT at T_TPW which are consistent with the slope discontinuity in the SPRT deviation functions. Since this discontinuity is by definition non-unique, and can take a range of values including zero, we suggest that mathematical representations of (T -T 90 ), such as those in the mise en pratique for the kelvin [2], should have continuity of d(T -T 90 )/dT at T_TPW.

Item Type: Article
Keywords: Acoustic gas thermometry, ITS-90, Thermodynamic temperature
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Divisions: Engineering, Materials & Electrical Science
Identification number/DOI: 10.1007/s10765-016-2176-4
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/7491

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